1. Field of the Invention
The present invention relates to a vertically moving device for vertically moving the vertically movable platform using wires.
2. Description of the Related Art
Vertically moving devices operate a spool mechanism for spooling wires to vertically move a vertically movable platform to a predetermined height by adjusting the amount of the wires that are fed out from the spool mechanism. For example, in a vertically moving device described in Patent Document 1, four single-line wires spooled by a spool mechanism are connected to the four corners of a vertically movable platform which is rectangular in plan view. The height of the vertically movable platform is controlled by adjusting the amount of the wires fed out from the spool mechanism.    Patent Document 1: Japanese Patent Application Publication No. H08-301410.
However, in the vertically moving device described in Patent Document 1, only one of the four single-line is sometimes stretched longer than the other three due to changes that occur over time. When that happens, the amount of wire fed out from the spool mechanism is longer for the stretched single-line wire than the amount of wires fed out from one of other three single-line wires. As a result, since the vertically movable platform is suspended and supported by the three remaining single-line wires, the vertically movable platform becomes unstable.